Polymerizable vinyl monomers undesirably polymerize during various stages of the manufacturing, processing, handling, storage and use thereof. It is well known that vinyl monomers readily polymerize and that such polymerization increases with concurrent temperature increases.
Common industrial methods for producing vinyl monomers include a variety of purification processes, including distillation to remove impurities. Unfortunately, purification operations carried out at elevated temperatures result in an increased rate of undesired polymerization. Polymerization such as thermal polymerization during the monomer purification process results not only in loss of desired monomer end product, but also in loss of production efficiency caused by polymer formation or agglomerization on process equipment. In heat requiring operations, such agglomerization adversely effects heat transfer efficiency.
Vinyl monomers may polymerize when left in storage tanks and during transportation at temperatures as low as room temperature. To prevent this polymerization from taking place, vinyl monomers are frequently treated with polymerization inhibitors.
A variety of compositions and methods have been proposed for inhibiting uncontrolled polymerization of vinyl monomers. For example, polymerization of acrylonitrile can be inhibited with phenothiazine, hydroquinone (HQ), methyl ether of hydroquinone (MEHQ), benzoquinone, methylene blue and combinations of hydroxyethylamine and phenylalene diamine. See, for example, U.S. Pat. No. 4,720,566. Polymerization inhibition of isoprene can be achieved by addition of tert-butylcatechol (TBC). TBC is also employed commercially to inhibit storage polymerization of butadiene and styrene.
U.S. Pat. No. 4,561,124 discloses the use of vitamin E as an inhibitor against premature polymerization initiation in reactive systems capable of undergoing a free radical initiated polymerization, which system before and/or after the polymerization thereof are placed in tissue contact with a living body. The reactive composition of concern in U.S. Pat. No. 4,561,124 are monocomponent or multicomponent medical and/or dental-medical adhesives, cements, or fillers based on conventional monofunctional and/or polyfunctional olefinically unsaturated compounds, particularly acrylic acid and/or methacrylic acids or derivatives thereof.
U.S. Pat. No. 5,159,106 discloses the use of a finely dispersed liquid phase containing inhibitors to stabilize reactive liquids in the production of (meth)acrylic acid. The finely dispersed liquid phase forms a continuous liquid film on the inner wall surfaces of the equipment. The inhibitors disclosed include hydroquinone, sterically hindered hydroquinone such as di-tert-butylhydroquinone and sterically hindered phenol compounds of the tocopherol type.